1. Field of the Invention
A fluid flow control system for use with a heat exchange apparatus, the fluid flow control system comprising a liquid flow control device operatively coupled between the condensor and evaporator and a vapor flow control device operatively coupled between the evaporator and compressor.
2. Description of the Prior Art
Numerous heating and cooling apparatus including condensors, compressors and evaporators have been developed for use with fluorocarbon refrigerants such as Freon. For example, U.S. Pat. No. 3,965,694 discloses an apparatus for heating or cooling including a first heat exchanger to transfer heat between the refrigerant and the atmosphere and a second subterranean heat exchanger to transfer heat between the earth and the refrigerant. A capillary tube restricting device is positioned in the refrigerant line between the first and second heat exchangers to liquefy the refrigerant before it reaches the subterranean heat exchanger. U.S. Pat. No. 2,513,373 discloses a heat pump for heating or cooling a fluid utilizing a closed circuit refrigerant loop. A closed circuit water line circulates water through a pair of subterranean heat exchangers. A heat exchanger which is coupled to both the closed circuit refrigerant loop and the closed circuit water line transfers heat energy between the independent water and refrigerant systems.
U.S. Pat. No. 2,529,154 discloses a solar heating system where water is circulated within a closed system coupled to a solar energy heat absorber while the refrigerant is circulated through a second closed system.
Other examples of the prior art are disclosed in U.S. Pat. Nos. 2,448,315; 2,693,939; 2,968,934; 3,175,370; 3,392,541; 3,564,862; 4,012,920; 4,049,407; France, No. 487762, and Sweden, No. 59350.
In these and in other conventional refrigeration and heat pump systems, superheat at the compressor inlet is poorly controlled or not controlled at all. This is especially true in systems having long evaporators or evaporators with a long time constant such as with ground source heat pumps where the evaporator comprises tubes inserted into the earth and/or water table in the earth.
In conventional ground source heat pumps, conventional thermal expansion valves, and electric expansion valves are subject to "hunting" wherein the superheat at the compressor inlet surges from a very high value such as 25.degree. F. to 35.degree. F., to zero with saturation and possibly "slugging" of the compressor. Use of capillary tubes or "automatic" expansion valves to control the Freon liquid flow requires sizing or adjusting such that saturation and "slugging" the compressor with liquid never occurs, and as a result, superheat runs excessively high during a large portion of the cycle with a corresponding loss of efficiency and tendency to over heat the compressor.
In conventional refrigeration and heat pump apparatus thermal expansion valves, automatic expension valves, electric expansion valves, and capillary tubes all fail to control the liquid Freon flow such that a given portion (bottom) of the condensor remains full of liquid to provide subcooling of the liquid, and prevent blow-through of uncondensed Freon from the condensor.
The subject invention provides such subcooling and blow-through control, with the additional desired result that liquid refrigerant flow from the condensor is at exactly the rate at which the condensor and the entire system is able to produce luqiud condensate.
The failure of conventional devices to properly control liquid flow from the condensor results in poorly controlled liquid flow into the evaporator and poorly controlled vapor flow from the evaporator. In other words, it is very important to control the rate of flow of the refrigerant liquid to the evaporator and refrigerant vapor from the evaporator to maximize vaporazation while minimizing superheating of the refrigerant vapor reaching the compressor. When the refrigerant is not completely vaporized (flow rate through evaporator too fast) the remaining liquid mist (unevaporated Freon) has a cooling or chilling effect on the vapor compressor chamber, drastically reducing efficiency, and can cause damage to the compressor. On the other hand, when the refrigerant is excessively superheated (flow rate through evaporator too slow) the superheated vapor can cause the compressor to overheat, and the compressor has less volumetric efficiency with a resulting loss in system efficiency due to overexpansion of the Freon vapor entering the compressor.
The subject invention provides a constant smooth flow of liquid refrigerant to the evaporator and a constant smooth flow of vapor refrigerant, of low superheat, from the evaporator to the compressor providing an efficient, effective and reliable fluid flow control system.